Increasingly, electronic circuit manufacturers need to reduce the power consumption of their boards. The conservation of power is particularly important in portable electronic devices, such as laptop or notebook computers, where the product is specifically designed for use in situations where power outlets are not available. Since laptop and notebook computers must operate using internal batteries or rechargeable battery packs for extended periods of time, the conservation of battery power becomes a primary concern.
In a laptop or notebook computer, the largest consumer of power is the display. The proportion of power consumed by the display will vary depending on the technology used. Thus, laptop and notebook computer manufacturers have disabled the power to the display during periods of inactivity. Decoupling the display from the power supply can be accomplished with fairly simple circuitry.
The next largest consumer of power on a laptop or notebook computer is the CPU motherboard microprocessor. Heretofore, computer manufacturers have used one or two techniques for reducing power consumption of the microprocessor during periods of inactivity. One technique reduces the speed of the system clock to a fraction of the normal operating frequency during periods of inactivity. Since the power consumption of the microprocessor is proportional to the frequency, reducing the frequency of the system clock also reduces the power consumption of the microprocessor. In an Intel 80386DX microprocessor (manufactured by Intel Corporation of Santa Clara, Calif.), reducing the operating frequency from 33 MHz to 4 MHz reduces the typical operating current of the microprocessor from 400 to approximately 100 milliamps. Nevertheless, an operating current of 100 milliamps still poses a large power drain on the battery.
A second technique for reducing power turns off the system clock during periods of inactivity. Turning off the system clock affects all circuitry on the motherboard. Consequently, the circuitry which disables the system clock must also save all pertinent information in the microprocessor and associated board logic and restore the data upon resumption of activity such that the state of the computer after resumption of the system clock will be identical to the state of the computer prior to disabling the system clock. As a result, this technique for consuming power is both costly because of the complicated circuitry and slow because of the need to store and restore the state of the computer.
Therefore, a need has arisen in the industry to provide a method and apparatus for conserving power in an electronic device which significantly reduces the power drain of the microprocessor without the need for complicated external circuitry.